Lysostaphin fermentation with accelerated time cycle

ABSTRACT

REDUCED FERMENTATION PERIODS ARE OBTAINED IN THE LYSOSTAPHIN FERMENTATION WHEN HEAT STERILIZATION OF THE MEDIUM IS ELIMINATED AND AN INOCULUM VOLUME OF FROM 2.5% TO 20% IS EMPLOYED. A CYCLIC PROCESS IN WHICH AN ALIQUOT OF ONE BATCH SERVES AS INOCULUM FOR THE NEXT IS DESCRIBED.

United States Patent Oifice Int. Cl. C12d 9/00 US. Cl. 195-96 6 Claims ABSTRACT OF THE DISCLOSURE Reduced fermentation periods are obtained in the lysostaphin fermentation when heat sterilization of the medium is eliminated and an inoculum volume of from 2.5% to 20% is employed. A cyclic process in which an aliquot of one batch serves as inoculum for the next is described.

The present invention is an improved fermentation process for the production of the antibiotic lysostaphin. Lysostaphin is an antibiotic having an enzymic nature which is specific for bacteria of the genus Staphylococcus. It is the subject of US. 3,278,378, patented Oct. 11, 1966, by C. A. Schindler and V. T. Schuhardt. An improved method for its production by fermentation is the subject of US. patent application Ser. No. 381,684, filed July 10, 1964, by Zygmunt and Browder, now US. Pat. No. 3,398,056, patented Aug. 20, 1968. The present invention deals with a still further improvement.

According to the Schindler, et al. patent, lysostaphin is produced by a new species of staphylococcus known as Staphylococcus staphylolyticus. A strain of this species is on deposit at the Northern Regional Research Laboratory in Peoria, 111., as NRRL B-2628. Conventional fermentation techniques employing submerged culture are used for its production, and are also the subject of the Schindler, et al. patent. The Zygmunt et al. patent application Ser. No. 381,684, refers to a lysostaphin fermentation process which employs a medium having a relatively high concentration of enzymatically hydrolyzed casein as organic nitrogen source and glycerol as carbon source and provides higher yields of the antibiotic.

According to prior lysostaphin fermentation techniques, which are referred to in the foregoing disclosures, the fermentation medium is prepared by dissolving or suspending the ingredients in water, heat sterilizing, and then inoculating with a culture of S. staphylolyticus. Conventionally, the inoculum volume has been about 0.1% to 1% the volume of the fermentation batch, The object of sterilization, of course, is to forestall the growth of contaminating organisms which reduces the production of antibiotic and sometimes produces unwanted metabolites which may interfere with recovery of the antibiotic.

The lysostaphin fermentation, being a bacterial fenmentation, differs in a number of respects from the more common antibiotic fermentations which employ fungi. For example, with lysostaphin production occurs during the log phase of growth rather than the stationary phase.

It has now been found that by use of a relatively large inoculum of a log phase culture of S. sraphylolyticus of from 2.5 to 20% of the batch volume, that the time required for production of the maximal concentration of lysostaphin is reduced from one-half to one-quarter that normally required and furthermore, that growth of the organism is so luxuriant and rapid that it is not necessary to sterilize the fermentation broth. Furthermore, improved yields are obtained by use of the non-sterile medium. It is believed that this is related not to the lack of sterility, but rather to the fact that heating of the medium is avoided. Heat sterilization, undoubtedly, has

3,594,284 Patented July 20, 1971 a hydrolytic or denaturing eifect on proteinaceous and other natural ingredients used in the broth. Evidently, the nutrients are presented to the microorganism in a more assimilable fashion it prior heating of the fermentation medium is avoided. This is presented as a theory and applicants do not intend to be bound by it. They are of the opinion that equally good fermentation yields could be obtained by using a broth sterilized by filtration in order to avoid heat sterilization, but this is not a practical suggestion due to the difiiculty of filtering a crude fermentation broth through presently available bacterial filters.

In its simplest form the present invention involves inoculating a conventional lysostaphin fermentation medium or one such as is described in the Zygmunt et al. application, containing an assimilable carbon source and an assimilable organic nitrogen source with from 2.5 to 20% by volume of a log phase inoculum culture of S. sta'phylolyticus. This results in a substantially reduced time cycle for the production of maximal lysostaphin titers in the fermentation broth. Prior fermentations have employed much smaller proportions of inoculum and fermentation periods of the order of 12 to 18 hrs. According to the present invention, use of the large inoculum volume results in maximal antibiotic production in from 4 to 8 hrs.

When this discovery was applied to a medium in which heat treatment was avoided in its preparation, that is, a medium for which the conventional heat sterilization step was omitted, a still further increase in antibiotic titer was obtained. These findings are illustrated in Example 1 which compares the use of a 1% inoculum volume (the prior art) with the use of 10% inoculum volume (this invention) in fermentations employing both heat sterilized media (the prior art) and media which were not heat sterilized (this invention).

Example 2 which follows describes a series of fermentations in which inocula ranging from 2.5 to 20% by volume of the medium were employed, again using a medium in which all previous heat treatment was avoided and no other sterilization means were employed. It is evident from the results in which a 2.5 inoculum volume was used in comparison with the results with a 1% inoculum volume (Example 1), that 2.5% approaches the minimum operable volume for a shortened fermentation cycle according to the present invention. Possibly a somewhat lower inoculum volume than 2.5% could be employed and the benefits of the present invention realized. Nevertheless, the preferred inoculum volume is from 10% to 20% since substantially higher lysostaphin yields in the shorter time cycle are obtained.

Example 3 illustrates a preferred embodiment of the present invention in which repeated fermentation cycles are conducted by using an aliquot of one batch to inoculate the next. Again heat treatment of the medium as in heat sterilization is avoided. When-reference to preparation of a fermentation medium Without the application of heat is made in this disclosure, what is intended is that at no time after the ingredients are mixed with 'water is the batch exposed to a temperature in excess of 50 C. This permits gentle warming to effect dissolution or dispersion of the ingredients but precludes the use of heat sterilization. In this experiment after the initial fermentation was completed by volume of the cultivated medium was removed for recovery of the antibiotic and 20% of the original volume was left in the fermenter to serve as inoculum for the succeeding cycle, The medium level was brought to its original value with fresh medium prepared in the same way as that employed in the first cycle and the cultivation was repeated as before. This was repeated four additional times for a total of five cycles. Satisfactory antibiotic titers were obtained in from 4 to 5 hrs. in each of the second, third, and fourth cycles but in the fifth cycle lower but still substantial titers were obtained. The maximum number of cycles that can be conducted in this fashion will vary with the specific equipment employed varying between 2.5% and 20%. Periodic assays as before were made. The results are arranged in the following table:

TABLE 2.EFFECT OF INOOULUM SIZE WITHOUT HEAT and other details, but generally speaking it is believed that STE RILIZAIION an initial cycle and three subsequent cycles for a total of 5 Dry cell Lysostaphin four batches is the maximum possible and it is preferred Inoculum Hours wciglht it titler not to carry the cyclic process further since lower yields volum" cumvated pH (mg/1n are obtained in subsequent cycles. 2 7.00 3.3 The following examples are given to further illustrate 3: g; the invention but they are not to be considered as the sole 10 20% 7 7.00 20.3 25. embodiments thereof nor limitative of the scope of the 3 $128 25:5 invention. 1( 32. 31.2 EXAMPLE 1 4 7.' 20 1418 4:3 6 7.05 28.3 225 Effect of inoculum size and heat sterilization of media 15 10% g: 23:2 1:; Eighty liters of fermentation medium having the fol- 3 $188 28:: 25 2 lowing composition were prepared in four equal por- 2 6.90 g1; pg tions contained in separate 10 gal. stainless steel fer- 5% g ,13% 16:2 menters. s 7. 10 27. g Percent y Weight 20 3 53% iia 1I0 Enzymatically hydrolyzed casein (NZ Amine E) 4.8 4 g t? -g y p pt0ne Phyt0ne) 0.5 25% 3 1 25, 1 17,5 Sodium Chloride 0.5 10 Dipotassium hydrogen phosphate 0.25 Dextrose 0,125 EXAMPLE 3 f Cyclic fermentation procedure a er .s.

q One hundred and fifty liters of nutrient medium having Two of the fermenters and contents were then heat the same composition as described in Example 1 was prester111zed at 118-122" C. for 45 min. No heat treatment pared. Thirty liters were set aside for the preparation of was applied to the other two except for the mild warminocula. Twenty-four liters thereof were then charged to mg to a temperature of about 50 C. to assist in dissolving a 10 gal, stainless steel fermenter and inoculated with 6 l. the lI1gICd1eI1tS. One of the sterilized fermenters and one of a log phase culture of S. staphylolyticus. Periodic of the non-sterilized fermenters was then inoculated with assays for lysostaphin activity were made. When it ap- 1% y Volume of a lOgphaSe culture of S. staphylolyticus. 35 peared that the maximal antibiotic titer had been obtained, The other two fermenters were inoculated with 10% by 24 l. of the mature culture medium was removed from volume of the same culture. The fermenters were then the fermenter and set aside for recovery of the antibiotic. aerated at the rate of 1 volume of air per minute, moni- The same volume of fresh medium was then added to the tor d for foaming, and the temperature controlled at 37 vessel and cultivation was continued as before. This was C. Periodic measurements of pH, dry cell weight, and 40 continued through five cycles. The results are arranged lysostaphin concentration were made. The results obin the following table. tained are arranged in the following table. TABLE 3 CYCLIC FERMENTATION PROCESS TABLE 1.EFFECT OF INOGULUM SIZE AND PRIOR HEAT Dry cell Lysostaphln STERILIZATION OF MEDIUM Hours weight titer Cycle No. cultivated pH (mg/ml.) (units/ml.) Dry cell Lysostaphin Inoeulum Hours weight ti r 2 7.05 5.3 2.7 volume cultivated pH (mg/ml.) (units/ml.) 1 4 7. 35 9. 3 3. 8 5 7.30 17.9 11.1 Non'sterile medium 7. 5 7. 25 28. 3 26. 5 2 7.40 15.8 6.2 10 7.4 20.7 3.7 2 4 7. 50 20.2 22.0 1% 11 7. 3 32. 9 s. 2 4. 5 7. 2 b 12 7.4 31.5 11.5 2 7. 40 15.3 5.0 2 7.15 4. 4 1. 3 3 4 7. 40 26. 4 17- 6 4 7. 50 10.2 2.0 4.5 7.50 10% 6 7. 30 18.1 5. s 4 5 6.80 30.1 1 8 s 7.15 29.7 24.4 2 7.25 148 3.6 10 7.70 32.9 24.5 55 5 4 5.75 23.7 10.0 6 7.55 30.5 11.2 Sterile medium 8 8.25 33.4 11.2

10 7.3 30.5 10.5 1% 11 7.2 33.9 18.6 In the foregoing examples the lysos p assays were 3 7- 2:; conducted as is described in the Schindler, et al. patent, 4 7. 50 13.4 517 U.S. 3,278,378. This is a photometric procedure in WhlCh 10% g :32 12 one unit of lysostaphin is defined as that amount 0513 89- 10 6.40 27.3 13.5 staphin which will cause a 50% reduction in turbidity 1n 10 minutes of a suspension of Staphylococcus aureus FDA 209P cells of specified concentration relative to an EXAMPLE 2 identical control suspension which is not exposed to the Comparison of various inocula ratios test sample of lysostaphm A photometnc procedure was also used to determine Four 10 gal. sta nless steel fermenters were prepared dry cell weights in the periodic assays reported above. A with a medium having the composition given in Example standard curve was employed from which the optical den- 1 each in an amount to provide a final batch volume of sity of a diluted fermentation broth could be related to 20 l. The media were warmed to dissolve the ingredients the dry cell mass contained therein. but temperatures in excess of 50 C. were avoided, and What is claimed is: the media were not heat sterilized. Each fermenter was 1. In a fermentation process for producing lysostaphin then inoculated with a different sized portion of inoculum by cultivation of a strain of Staphylococcus staphylolyticus to provide a final volume in each of 20 l. with inocula on an aqueous nutrient medium containing assimilable sources of carbon and organic nitrogen, the improvement which comprises inoculating a volume of said nutrient medium which has at no time prior to employing it in said process been subjected to a temperature in excess of 50 C. with an amount of S. staphylolyticus inoculum culture having a volume of from 2.5% to 20% the total volume of inoculated medium.

2. The process of claim 1 wherein said inoculum culture has a volume of from to the volume of said medium after inoculation.

3. The process of claim 1 wherein said inoculum culture is an aliquot of a previous lysostaphin fermentation batch prior to harvest of the lysostaphin therefrom.

4. The cyclic fermentation process for the production of lysostaphin which comprises:

(a) an initial cycle comprising inoculating an aqueous nutrient medium containing assimilable sources of carbon and organic nitrogen which has at no time prior to employing it in the process been subjected to a temperature in excess of 50 C. With from 2.5% to 20% by volume of inoculated medium of an S. staphylolytic'us inoculum culture, cultivating said inoculated medium in a fermentation vessel at a temperature of to 40 C. until substantial lysostaphin is produced, and;

(b) removing from to 97.5% by volume of resulting cultivated medium from said vessel, and; (c) a subsequent cycle comprised of charging to the residual cultivated medium in said vessel fresh medium of similar constitution cultivating as specified in (a), and removing cultivated medium as specified in (b) and; (d) repeating (c). 5. The process of claim 4 wherein from 80% to of said medium is removed in step (b).

6. The process of claim 4 wherein said subsequent cycle is repeated to provide up to three of said subsequent cycles following a single initial cycle.

References Cited UNITED STATES PATENTS 3,278,378 10/1966 Schindler et al. l8OX A. LOUIS MONACELL, Primary Examiner S. RAND, Assistant Examiner U.S. Cl. X.R.

l95l00; 4241l5 

